Exchange Online turns off SMTP AUTH Basic by default in December

At the end of December 2026, Microsoft will disable SMTP AUTH Basic authentication by default for existing Exchange Online tenants, and new tenants won't get it at all. Mail sent with a username and password will be rejected with a permanent 550 5.7.30 error, with final removal planned for the second half of 2027.

• The change hits existing tenants at the end of December 2026
• Error 550 5.7.30 is a permanent rejection with no queue or retry
• Final removal of SMTP AUTH Basic will be announced in H2 2027
• Alternatives include OAuth 2.0, IP-based relay and Graph sendMail